BACKGROUND: Investigations based on quantitative sensory testing have consistently shown evidence of allodynia in fibromyalgia syndrome (FMS) patients involving both the spinal and supraspinal pain regulatory systems. Functional imaging studies have demonstrated enhanced neural activities in pain-related brain areas as well as impairment of pain inhibition in the descending nociceptive regulatory system. A higher state of excitability of spinal nociceptive neurons as evidenced by lowered nociceptive flexion reflex R-III (NFR) threshold was reported for FMS patients. The NFR procedure has been shown to be a valuable tool to evaluate pharmacologically active therapeutic agents at the spinal level.

OBJECTIVE: Serotonin-noradrenaline reuptake inhibitors have been shown to reduce pain in FMS patients possibly through descending monoaminergic pain pathways modulation. This randomized double-blind placebo-controlled trial assessed the pharmacodynamic activity of the dual-reuptake inhibitor milnacipran (MLN) at the spinal level by means of the objective spinal NFR.

CONCLUSION: Milnacipran has a predominantly supraspinal analgesic effect as evidenced by the significant clinical benefits and the absence of changes in the nociceptive spinal reflex threshold. Higher dose was associated with higher pain reduction. Reported analgesia was independent of patients' emotional status.